Arrangement for feeding wood in a pulp grinder

ABSTRACT

An arrangement in a pulp grinder comprising a grindstone, a feed chute extending to the grindstone, a piston moving in the feed chute, an auxiliary piston and closing members. In the arrangement, there are recesses on the front of the piston and apertures in the auxiliary piston so that the closing members can be pushed from both sides of the feed chute through the auxiliary piston to the recesses of the piston so that they settle behind the wood pressed by the piston.

FIELD OF THE INVENTION

The invention relates to an arrangement for feeding wood in a pulpgrinder comprising a grindstone, a feed chute extending to thegrindstone, a piston moving in the feed chute to press the wood againstthe grindstone, and a closing member to prevent the wood from movingaway from the grindstone when the piston is moved away from thegrindstone so as to allow the feed of a new batch of wood.

BACKGROUND OF THE INVENTION

When wood is ground to produce fibres, the grinders typically used aregrinders in which the blocks of wood are pressed against the surface ofa rotary grindstone, simultaneously spraying water there to produce apulp suspension. The most generally, the wood supply is implemented inpulp grinders on a discontinuous basis: one batch of wood at a time isfed into a feed chute, after which the wood in the feed chute is pressedby a cylinder and a piston against the grindstone. In order that theoutput would be as great as possible, two feed chutes, with cylinders,are usually arranged on the opposite side, of the grindstone.Consequently, when a feed chute is being filled, the grindstone issubjected to less load than when both the feed chutes are in thegrinding step, and this causes both uneven loading and variation in thequality of the ground pulp. Further, the drawback of the discontinuoussupply is that the output is smaller when the wood is fed in batchesthan when continuous grinding is used. Another problem in thediscontinuous grinding is that the blocks of wood fed during thecompression press more firmly against each other, which also results invariation between the production rates at the beginning and at the endof the grinding. Consequently, for example the freeness of the groundpulp is higher at the beginning of the compression, dropping toward theend of the furnace, even if the feed rate at the piston of the cylinderis adjusted to remain constant. For the same reason, the motor is loadedunevenly.

Previously known are also continuous grinders in which the continuouswood supply is based on moving feed chains on both sides of a feed chuteand on the weight of the wood in the feed chute. Such a grinder isknown, for example, from German Offenlegungsschrift 28,12,299. Thedrawback of the solution is that to provide the continuous wood supplyand sufficient compression, the chains must be rather long, which inpractice means that the feed chute must be up to 6-8 metres high. Thecontact surface between the chains and the blocks of wood that are beingfed is thus sufficiently large, and the weight of the pile of woodsimultaneously helps to press the wood against the feed chains forcompression. Because of this, only an essentially upright feed chute canbe used in the grinding process, which notably restricts the amount ofwood that can be ground simultaneously. As a result, the capacity of thegrinder is naturally smaller than in solutions where wood fed from twoor more feed chutes can be ground simultaneously. Another problem in thehigh feed chute is that the blocks of wood may settle obliquely, whichaffects the grindstone and because of which the grinder must besharpened unduly often in order to correct the obliqueness. Since thepressing force of the chains does not divide evenly between the blocksof wood in the feed chute, but in practice the blocks of wood that arethe closest to the chains are fed at a higher feed rate than those inthe middle of the feed chute, this affects the quality and may alsocause the above obliqueness.

European Patent 266,582 teaches a solution comprising one or twoauxiliary pistons in addition to the actual pressing piston, theauxiliary pistons being pushed by separate feed cylinders toward thegrindstone when the actual pressing piston is moved to the startingposition of its stroke to allow the feed of a new batch of wood. In thisembodiment, a separate closing trap is to be pushed in between theactual piston to prevent the wood from moving backward with the piston.The closing trap is to be pushed between the piston and the wood as thepiston presses the wood, whereby the closing trap would have to bepushed to its place under great compression. In practice, this is notpossible since the frictional forces caused by the pressing force are sogreat that the solution is impossible to implement. Correspondingly, ifthe piston were pulled back first, the operation of the trap and thegrinding process would be essentially impaired.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement bywhich essentially continuous grinding can be provided under essentiallyconstant grinding conditions, even though the wood is fed into thegrinder in batches. The arrangement of the invention is characterized inthat the piston comprises at least one recess into which the closingmember can be pushed so that when the closing-member is in the feedchute, the feed chute is closed crosswise of the wood to be ground sothat the backward movement of the wood is essentially prevented when thepiston moves backward. The essential idea of the invention is that theinvention comprises closing members on one or both sides of the feedchute, and that as the piston presses the wood the closing members canbe pushed into the recesses of the pressing piston to close the feedchute, whereby the wood will not be able to move backward from thecompression with the piston as the piston moves to the starting positionof its stroke to allow the feed of a new batch of wood. It is theessential idea of a preferred embodiment of the invention that theinvention comprises at least one auxiliary piston and that the closingmembers can be pushed through each auxiliary piston and that eachauxiliary piston can move in relation to the closing members, theauxiliary members having such apertures that the wood between theclosing members and the grindstone can be pressed by the auxiliarypistons so that the grinding continues essentially unchanged even when anew batch of wood is being fed in front of the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference tothe attached drawing wherein

FIGS. 1a to 1d show a schematic sectional side view of an embodiment ofthe arrangement according to the invention,

FIGS. 2a to 2d show a schematic sectional side view of anotherembodiment of the arrangement according to the invention, and

FIGS. 3a and 3b show a schematic view of alternative embodiments of theclosing members and the shape of the piston and the auxiliary piston inthese embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1a shows a schematic view of a grinder comprising a grindstone 1and a feed chute 2 extending to it. In the feed chute 2 there are blocksof wood 3, which are pressed by a piston 5 connected to a feed cylinder4 against the grindstone 1. Further, FIGS. la to 1d show two auxiliarypistons 6, which are arranged between the piston 5 and the feed chute 2on both sides of the piston. The grinder also comprises closing members7 on both sides of the feed chute 2. The closing members can be moved byclosing cylinders 8 crosswise of the feed chute 2 so that when they arein the `in` position, they essentially reach each other, preventing thewood 3 in the feed chute 2 from moving away from the grindstone 1. Thepiston 5 comprises one or more recesses for receiving the closingmembers 7, the closing members 7 pushing between the wood 3 and thepiston 5 into the recesses. Further, the auxiliary pistons 6 compriseapertures 6a, through which the closing members 7 extend and can pushinto the movement range of the piston 5. The length of the apertures 6ais such that the auxiliary pistons 6 can move a desired distance intheir longitudinal direction in relation to the feed chute 2. Theauxiliary pistons 6 can thus push the wood by the effect of auxiliarycylinders 9 toward the grindstone 1.

FIG. 1a shows a situation where the wood in the feed chute, tightlycompressed by the piston 5, is ground by the rotating grindstone so thatfibre is detached. The closing members 7 are inserted in the feed chute2, thereby preventing the wood 3 from moving away from the grindstone 1.The auxiliary pistons 6 are moved toward the grindstone 1 by theauxiliary cylinders 9, whereby the auxiliary pistons, upon moving,compress the wood between the closing means 7 and the grindstone in thefeed chute 2 and thereby effect essentially continuous compressionbetween the wood 3 and the grindstone 1. Simultaneously, the piston 5 isin its extreme position, the furthest away from the grindstone 1, and anew batch of wood 3' has been fed in front of it, for example, in themanner described in Finnish Patent 69,653 or in some other solutionknown per se. FIG. 1b, in turn, shows a situation where the piston 5 hasbeen pushed toward the grindstone 1 by the feed cylinder 4 so that thebatch of wood 3' pressing against the closing members 7 is beingcompressed. When the batch of wood 3' has compressed to a sufficientdegree, the closing members 7 are slowly pulled away from the feed chute2 by the closing cylinders 8, whereas the piston 5 and the auxiliarypistons 6 continue to move toward the grindstone 1. When the batch ofwood ' has been compressed sufficiently tightly, the wood 3 is continuedto be pressed by the piston 5, but the auxiliary pistons 6 are slowlypulled backward, i.e. away from the grindstone, by the auxiliarycylinders 9, until the situation illustrated by FIG. 1d is achieved. InFIG. 1d, the auxiliary pistons are the furthest away from the grindstone1, and the piston 5 is the closest to the grindstone 1. The closingmembers 7 are then pushed into the feed chute by the closing cylinders 8so as to prevent the backward movement of the wood, and the cycle ofoperation will restart in the manner described in connection with FIG.1a. As shown in the figure, the closing members 7 are symmetrical inrelation to the feed chute 2 and thereby also the piston 5, and theynarrow toward the centre of the feed chute, whereby they are easy topull away from between the blocks of wood. Further, the pushing surfaceof the piston 5 is naturally such that it essentially corresponds withthe shape of the heads of the closing members 7. Alternatively, thatsurface of the closing members which is close to the grindstone 1 can bestraight, and those surfaces of the piston 5 which come into contactwith the wood can also be straight.

The advantage of the arrangement is that the compression of the woodpressed against the grindstone 1 and the grinding conditions can bemaintained essentially constant, whereby the motor power of the grindercan be set to be essentially constant in a desired manner. The grindingconditions are maintained essentially unchanged, and the quality of thefibre obtained and the output of the grinder can be maintained constantin a desired manner. The feed chute of the grinder can thus be shorterand the dimensions of the grinder can thereby be smaller than in thepreviously known continues grinders, and one or more feed chutes withthe necessary components can be arranged around one and the samegrindstone to maximize the capacity of the grinder.

FIGS. 2a to 2d show an embodiment that is otherwise similar to that ofFIG. 1 except that only one auxiliary piston 6 and one closing member 7are used therein.

FIGS. 3a and 3b, in turn, show the cross-sections of two differentembodiments of the closing members and the corresponding shapes of thepiston 5 and the auxiliary pistons 6, seen from the same direction. InFIG. 3a the closing member 7 is a single continuous sheet-likecomponent, whereby the piston 5 comprises, at the edges, two presssurfaces 5a pressing the wood and between the surfaces a recess 5bessentially corresponding in shape with the closing member 7. Theauxiliary piston 6 comprises an elongated aperture 6a in the middle, theaperture being wider than the closing member 7 and its length in thelongitudinal direction of the auxiliary piston 6 being such that theauxiliary piston can move a sufficient distance. FIG. 3b, in turn,illustrates an embodiment comprising either two separate closing membersarranged in parallel or one continuous fork-like unit comprising twoclosing members. In this embodiment, the piston 5 comprises three presssurfaces 5a pressing the wood and two recesses 5b between them, theshape of the recesses being such that the parallel closing members canpush into the piston 5, between the piston and the wood. The auxiliarypiston 6 comprises two apertures 6a, the distance between the aperturesand the width of the apertures being such that the closing members canpush through the apertures. The length of the apertures 6a is such thatthe auxiliary piston 6 can move a desired distance in relation to theclosing members.

As shown in FIGS. 1a to 1d and 2a to 2a, the closing members arearranged on those sides of the feed chute 2 which are essentiallyparallel to the axle of the grindstone 1. Both the closing members 7 andthose surfaces of the piston 5 which come into contact with the wood 3are therefore crosswise of the axle of the grindstone 1, so that whenthe wood is parallel to the axle of the grindstone, as usual, theclosing members 7 and those surfaces of the piston 5 which come intocontact with the wood are also crosswise of the wood.

The above description and the drawings present the invention only by wayof example, without limiting it in any way. There may be one or moreclosing members on both sides of the feed chute. Also, the closingmembers in the crosswise direction of the feed chute can either becontinuous or consist of several parts, and the apertures of theauxiliary pistons and the recesses of the piston must be designedaccordingly. The invention is not limited to a pulp grinder of a certaintype. It can thus be used in both non-pressure grinders and pressuregrinders, the other necessary operations and apparatuses beingimplemented conventionally in a previously known manner so that they aresuited to the solutions in question.

What is claimed is:
 1. An arrangement for feeding wood in a pulp grinderof the type having a grindstone, a feed chute extending to thegrindstone, and a piston that is slidable within the feed chute and hasan end face configured to press the wood against the grindstone saidarrangement comprising:at least one closing member that is movable intothe feed chute crosswise of the wood to prevent the wood from movingaway from the grindstone when the piston is moved away from thegrindstone so as to allow a new batch of wood to be fed into the feedchute between the face of the piston and the closing member, and the endface of the piston defining at least one recess into which the at leastone closing member can be pushed while the end face of the piston ispressing the wood against the grindstone, so that when the at least oneclosing member is pushed in the feed chute, the feed chute is closedcrosswise of the wood to be ground so that backward movement of the woodis essentially prevented when the piston moves backward.
 2. Thearrangement according to claim 1, further comprising at least oneauxiliary piston slidably disposed within the feed chute for pressingthe wood against the grindstone, the auxiliary piston defining at leastone aperture that extends therethrough in a direction crosswise of thewood so that the at least one closing member can be pushed through theauxiliary piston each aperture of the auxiliary piston having a lengthin the travel direction of the auxiliary piston that is sized such thatwhen the at least one closing member is pushed through the aperture toclose the feed chute, the auxiliary piston can be moved toward thegrindstone to press the wood continuously against the grindstone.
 3. Thearrangement according to claim 2, wherein two closing members aredisposed on opposite sides of the feed chute and two auxiliary pistonsare slidably disposed within the feed chute on opposite sides of thepiston each auxiliary piston defining an aperture such that the closingmembers can be pushed through the apertures to close the feed chute. 4.The arrangement according to claim 1, comprising a single closing memberformed as a continuous closing member, and wherein the piston comprisesa single recess extending crosswise of the piston in a travel directionof the closing member.
 5. The arrangement according to claim 1,comprising at least two closing members disposed on at least one side ofthe feed chute, the closing members being spaced apart in a crosswisedirection of the piston and the piston defining an equal number ofrecesses as there are closing members in the crosswise direction of thepiston.
 6. A pulp grinder for grinding wood to make wood pulp,comprising:a grindstone; a feed chute extending to the grindstone; apiston that is slidably disposed within the feed chute and has an endface configured to press the wood against the grindstone; at least oneclosing member that is movable into the feed chute crosswise of the woodto prevent the wood from moving away from the grindstone when the pistonis moved away from the grindstone so as to allow a new batch of wood tobe fed into the feed chute between the end face of the piston and theclosing member; and the end face of the piston defining at least onerecess into which the at least one closing member can be pushed whilethe end face of the piston is pressing the wood against the grindstone,so that when the at least one closing member is pushed into the feedchute, the feed chute is closed crosswise of the wood so that backwardmovement of the wood is essentially prevented when the piston movesbackward.